Actions: Add Redis and Redis Sentinel services

This adds Redis and Redis Sentinel services to the GitHub Actions test
setup. The current library we're using to mock the Redis connection
doesn't support Sentinel connections, so we have no simple way to test
that with a mock.

.github/workflows/default.yml

@@ -20,6 +20,30 @@ jobs:
           --health-timeout 5s
           --health-retries 5
 
+      redis:
+        image: redis
+        ports:
+          - 6379:6379
+        options: >-
+          --health-cmd "redis-cli ping"
+          --health-interval 10s
+          --health-timeout 5s
+          --health-retries 5
+
+      redis-sentinel:
+        image: bitnami/redis-sentinel
+        env:
+          REDIS_MASTER_HOST: redis
+          REDIS_MASTER_SET: data
+          REDIS_SENTINEL_QUORUM: 1
+        ports:
+          - 26379:26379
+        options: >-
+          --health-cmd "redis-cli -p 26379 ping"
+          --health-interval 10s
+          --health-timeout 5s
+          --health-retries 5
+
     env:
       PGHOST: localhost
       PGUSER: postgres